[clang] [clang-repl] Simplify the logic around out of process execution. NFC (PR #175322)

[NAKAMURA Takumi via cfe-commits]

chapuni wrote:

@vgvassilev Excuse me, I am seeing on my private bootstrapping builder.

`InterpreterTestBase.FindRuntimeInterface` and `InterpreterTestBase.SanityWithRemoteExecution` are failing. They could be improved when I added `lib/clang/{ver}/lib/{triple}` in clangInterpreter.

https://github.com/llvm/llvm-project/pull/175322